Maps and cartograms of the 2004 US presidential election results

Michael Gastner, Cosma Shalizi, and Mark Newman
University of Michigan

Email: Thanks to everyone who wrote to us about the maps. We've had
over a million hits on the web page and received so much email that we may
not be able to reply to everyone, but we much appreciate all your comments
and suggestions. Most of the things people have been asking about are
answered in this list of frequently asked questions.

Election results by state

On election night and in the months since then, we have seen many maps that
look like this (click on any of the maps for a larger picture):

The (contiguous 48) states of the country are colored red or blue to
indicate whether a majority of their voters voted for the Republican
candidate (George W. Bush) or the Democratic candidate (John F. Kerry)
respectively. The map gives the superficial impression that the "red
states" dominate the country, since they cover far more area than the blue
ones. However, as pointed out by many others, this is misleading because
it fails to take into account the fact that most of the red states have
small populations, whereas most of the blue states have large ones. The
blue may be small in area, but they are large in terms of numbers of
people, which is what matters in an election.

We can correct for this by making use of a cartogram, a map in which
the sizes of states have been rescaled according to their population. That
is, states are drawn with a size proportional not to their sheer
topographic acreage -- which has little to do with politics -- but to the
number of their inhabitants, states with more people appearing larger than
states with fewer, regardless of their actual area on the ground. Thus, on
such a map, the state of Rhode Island, with its 1.1 million inhabitants,
would appear about twice the size of Wyoming, which has half a million,
even though Wyoming has 60 times the acreage of Rhode Island.

Here are the 2004 presidential election results on a population cartogram
of this type:

The cartogram reveals what we know already from the news: that the country
was actually very evenly divided by the vote, rather than being dominated
by one side or the other.

The presidential election is not decided on the basis of the number of
people who vote each way, however, but on the basis of the electoral
college. Each state contributes a certain number of electors to the
electoral college, who vote according to the majority in their state. The
candidate receiving a majority of the votes in the electoral college wins
the election. The electoral votes are apportioned roughly according to
states' populations, as measured by the census, but with a small but
deliberate bias in favor of smaller states.

We can represent the effects of the electoral college by scaling the sizes
of states to be proportional to their number of electoral votes, which
gives a map that looks like this:

This cartogram looks very similar to the one above it, but it is not
identical. Wyoming, for instance, has approximately doubled in size,
precisely because of the bias in favor of small states.

The areas of red and blue on the cartogram are now proportional to the
actual numbers of electoral votes won by each candidate. Thus this map
shows at a glance both which states went to which candidate and which
candidate won more votes -- something that you cannot tell easily from the
normal election-night red and blue map.

Election results by county

But we can go further. We can do the same thing also with the county-level
election results and the images are even more striking. Here is a
map of US counties, again colored red and blue to indicate Republican and
Democratic majorities respectively:

Similar maps have appeared in the press, for example in USA
Today, and have been cited as evidence that the Republican party
has wide support. Again, however, a cartogram gives a more accurate
picture. Here is what the cartogram looks like for the county-level
election returns:

Again, the blue areas are much magnified, and areas of blue and red are now
nearly equal. However, there is in fact still more red than blue on this
map, even after allowing for population sizes. Of course, we know that
nationwide the percentages of voters voting for either candidate were
almost identical, so what is going on here?

The answer seems to be that the amount of red on the map is skewed because
there are a lot of counties in which only a slim majority voted Republican.
One possible way to allow for this, suggested by Robert
Vanderbei at Princeton University, is to use not just two colors on the
map, red and blue, but instead to use red, blue, and shades of purple to
indicate percentages of voters. Here is what the normal map looks like if
you do this:

And here's what the cartogram looks like:

In this map, it appears that only a rather small area is taken up by true
red counties, the rest being mostly shades of purple with patches of blue
in the urban areas.

A slight variation on the same idea is to use a nonlinear color scale like
this:

These maps use a color scale that ranges from red for 70% Republican or
more, to blue for 70% Democrat or more. This is sort of practical, since
there aren't many counties outside that range anyway, but to some extent it
also obscures the true balance of red and blue.

Finally, if you found the maps on this page interesting, you might be
interested in this page also,
which contains a collection of cartograms of the entire world, depicting
all sorts of different things. It's nothing to do with the election, but
it's worthwhile reading nonetheless.

Notes:

Frequently asked questions (FAQs): A list of frequently asked
questions concerning our maps, along with answers, can be found here.

Correction: The figures for numbers of counties voting Rep/Dem were
off because of a bug in one of our programs. We've fixed this and
corrected the text above. Thanks to K. Drum and others for pointing this
out. (All the actual maps were fine however.)

Update: We've done some slight improvements to the cartograms,
based on updated population and electoral data. (You'll have to look
pretty hard to see any difference though.)

Update: We changed the color scale on the purple maps to be the same
as that used by Robert
Vanderbei. The old maps are still available above for those who are
interested.

Wallpapers: By popular demand, all of the maps are now available in
"wallpaper" sizes for your computer desktop. Click here.

Correction: The colors of a few counties in Texas and in Delaware
got swapped around because of differences in the alphabetizing of lists of
election returns. This is fixed now on all the maps. Thanks to
J. Henderson and S. Hughes for spotting the problems and letting us know.

Update: We've added a cartogram with areas of states proportional to
the number of votes they have in the electoral college.